Imaging device and focusing control method

ABSTRACT

An imaging device includes an image pick-up device including phase difference detection pixel pairs, each formed from a pair of phase difference detection pixels respectively having their openings eccentrically formed on opposite sides of a main axis of an imaging lens, and imaging pixel pairs; a reading section that reads out signals from the pixels arrayed in the image pick-up device using a rolling shutter method; a first correlation computation section that performs correlation computation on the signals from the phase difference detection pixel pairs; a second correlation computation section that performs correlation computation on the signals from the imaging pixel pairs; a correction section that corrects a result from the first correlation computation section using a result from the second correlation computation section; and a focusing section that performs focus control using the corrected result.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 13/966,859,filed on Aug. 14, 2013, which is a continuation application ofInternational Application No. PCT/JP2011/078194, filed on Dec. 6, 2011,the disclosure of which is incorporated herein by reference in itsentirety. Further, this application claims priority over Japanese PatentApplication No. 2011-080032, filed on Mar. 31, 2011, the disclosure ofwhich is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging device and a focusingcontrol method, and in particular to an imaging device and focusingcontrol method that perform focus control during imaging of a subject.

2. Related Art

Recently, accompanying increasing resolution of solid state imagepick-up devices such as Charge Coupled Device (CCD) area sensors andComplementary Metal Oxide Semiconductor (CMOS) image sensors, there is arapid increase in demand for information equipment with imagingfunctions, such as digital electronic still cameras, digital videocameras, mobile phones, and Personal Digital Assistants (PDAs, mobiledata terminals). Information equipment with imaging functions such asthose described above will be referred to in general as imaging devices.

Focusing control methods for detecting the distance to a main subjectinclude contrast methods and phase difference Auto Focus (AF) methods.Phase difference AF methods are often employed in various imagingdevices due to being able to detect the in-focus position faster and athigher precision than with contrast methods.

A rolling shutter method in which sequential resetting and reading isperformed from the upper sensors is known as a reading method used inimaging devices equipped with CMOS sensors. Since time differences arisein read timing according to the pixel position in a rolling shuttermethod, distortion may arise in an image of a subject in cases of movingsubjects.

Therefore, in a case in which a phase difference AF method is used forfocus control in an imaging devices equipped with CMOS sensors whenimaging a moving subject, there is an influence from distortion causedby the rolling shutter method, and errors may arise in phase differencedetection due to image movements or image changes that occur duringshifted read timings.

Japanese Patent Application Laid-Open (JP-A) No. 2009-128579 discloses adevice that, in cases in which a reliable focusing detection result hasnot been obtained by focus detection pixels disposed in a horizontaldirection, performs focus detection with focus detection pixels disposedin a vertical direction, and in cases in which movement of the subjectis detected, prevents the focus detection with the focus detectionpixels disposed in the vertical direction.

JP-A No. 2008-72470 and JP-A No. 2008-263352 disclose devices thatcontrol the charge accumulation timing for pixels for phase differencedetection to be the same time.

However, the technology disclosed in JP-A No. 2009-128579 is merelytechnology in which focus detection is only performed using a phasedifference AF method under limited conditions, such as according to thereliability of a focus detection result or cases in which movement ofthe subject has not been detected, and is not capable of reducing theinfluence caused by a rolling shutter method performed during focusdetection by phase difference AF method. Moreover, since the technologydisclosed in JP-A No. 2008-72470 and JP-A No. 2008-263352 requires anadditional circuit, it increases cost.

SUMMARY

In consideration of the above circumstances, the present inventionprovides an imaging device and a focusing control method that, even incases in which detection of in-focus position is performed from signalsthat have been read from phase difference detection pixels disposed indifferent lines using a rolling shutter method, are capable of focuscontrol that reduces the influence of distortion caused by the rollingshutter method and detects the in-focus position at high precision,without provision of an additional circuit.

A first aspect of the present invention is an imaging device including:an image pick-up device including plural phase difference detectionpixel pairs, each formed from a first phase difference detection pixelhaving an opening eccentrically formed on one side with respect to amain axis of an imaging lens and a second phase difference detectionpixel having an opening eccentrically formed on the other side withrespect to the main axis, and plural imaging pixel pairs includingplural imaging pixels; a reading section that performs read-out withrespect to the image pick-up device by reading signals from the imagingpixels and the phase difference detection pixels arrayed in the imagepick-up device using a rolling shutter method; a first correlationcomputation section that performs correlation computation on the signalsthat have been read from the phase difference detection pixel pairs; asecond correlation computation section that performs correlationcomputation on the signals that have been read from the imaging pixelpairs; a correction section that corrects a correlation computationresult from the first correlation computation section using acorrelation computation result from the second correlation computationsection; and a focusing section that performs focus control using thecorrected correlation computation result.

Since the correlation computation result of the signals read from thephase difference detection pixel pairs is corrected with the correlationcomputation result of the signals read from the imaging pixel pairs, theinfluence of distortion caused by the rolling shutter method is reduced,and is it possible to perform in-focus position detection and focuscontrol at high precision, without providing an additional circuit.

In the above aspect, the second correlation computation section mayperform correlation computation on signals read from the plural imagingpixel pairs, each of which is formed from: an imaging pixel disposed ona line on which the first phase difference detection pixel of one of theplural phase difference detection pixel pairs is disposed, and animaging pixel disposed on a line on which the second phase differencedetection pixel of the one of the plural phase difference detectionpixel pairs is disposed.

In the above aspect, the second correlation computation section mayperform correlation computation on signals read from the plural imagingpixel pairs, each of which are formed from imaging pixels that aredisposed on lines that are different from the lines on which the phasedifference detection pixels of the plural phase difference detectionpixel pairs are disposed.

In the above aspect, the second correlation computation section mayperform correlation computation on signals read from the plural imagingpixel pairs provided with color filters of a same color as a color ofcolor filters provided at the plural phase difference detection pixelpairs.

In the above aspect, the second correlation computation section mayperform correlation computation on signals read from the plural imagingpixel pairs, which include an imaging pixel pair provided with colorfilters of a different color from a color of color filters provided atthe plural phase difference detection pixel pairs.

In the above aspect, the plural imaging pixel pairs may include one ormore imaging pixel pairs provided with R color filters, one or moreimaging pixel pairs provided with G color filters, and one or moreimaging pixel pairs provided with B color filters, and the secondcorrelation computation section may perform correlation computation onsignals that are read from one or more imaging pixel pairs of the pluralimaging pixel pairs which are formed from imaging pixels provided withcolor filters of a color having a signal level closest to a signal levelof the phase difference detection pixels forming the plural phasedifference detection pixel pairs.

The above aspect may further include: a selection section that, prior tothe correlation computation performed by the second correlationcomputation section, selects from the plural imaging pixel pairs, whichinclude one or more imaging pixel pairs provided with R color filters,one or more imaging pixel pairs provided with G color filters and one ormore imaging pixel pairs provided with B color filters, one or moreimaging pixel pairs formed from imaging pixels provided with colorfilters of a color having a signal level closest to a signal level ofthe phase difference detection pixels forming the plural phasedifference detection pixel pairs; and a control section that controlsthe reading section such that signals are respectively read from theplural phase difference detection pixel pairs and the one or moreimaging pixel pairs selected by the selection section, wherein thesecond correlation computation section performs the correlationcomputation on the signals read under control of the control section.

The above aspect may further include an exposure control section thatcontrols an exposure time of the image pick-up device such that anexposure amount corresponds to the sensitivity of the imaging pixels.

The above aspect may further include: a determination section thatdetermines whether or not correction is to be performed by thecorrection section based on at least one of: a size of a focal regionfor focus matching, a number of the phase difference detection pixelsfrom which signals used in correlation computation by the firstcorrelation computation section are read out, movement of a subjectwithin an image capture angle, or movement of a subject within the focalregion, wherein, if the determination section determines that correctionis not to be performed by the correction section, the focusing sectionprevents execution of the correction by the correction section andperforms focus control using the correlation computation result from thefirst correlation computation section without correction.

Another aspect of the present invention is a focusing control method foran imaging device including an image pick-up device including pluralphase difference detection pixel pairs each formed from a first phasedifference detection pixel having an opening eccentrically formed on oneside with respect to a main axis of an imaging lens and a second phasedifference detection pixel having an opening eccentrically formed on theother side with respect to the main axis, and plural imaging pixel pairsincluding plural imaging pixels, the focusing control method including:performing reading-out to the image pick-up device by reading signalsfrom the imaging pixels and the phase difference detection pixelsarrayed in the image pick-up device using a rolling shutter method;performing a first correlation computation on the signals that have beenread from the plural phase difference detection pixel pairs; performinga second correlation computation on the signals that have been read fromthe plural imaging pixel pairs; correcting a result of the firstcorrelation computation using a result of the second correlationcomputation; and performing focus control using the corrected result ofthe correlation computations.

In the above aspect, the second correlation computation may includeperforming correlation computation on signals read from the pluralimaging pixel pairs, each of which is formed from: an imaging pixeldisposed on a line on which the first phase difference detection pixelof one of the plural phase difference detection pixel pairs is disposed,and an imaging pixel disposed on a line on which the second phasedifference detection pixel of the one of the plural phase differencedetection pixel pairs is disposed.

In the above aspect, the second correlation computation may includeperforming correlation computation on signals read from the pluralimaging pixel pairs each formed from imaging pixels that are disposed onlines that are different from lines on which the phase differencedetection pixels of the plural phase difference detection pixel pairsare disposed.

In the above aspect, the second correlation computation may includeperforming correlation computation on signals read from the pluralimaging pixel pairs, which are provided with color filters of a samecolor as a color of color filters provided at the plural phasedifference detection pixel pairs.

In the above aspect, the second correlation computation may includeperforming correlation computation on signals read from the pluralimaging pixel pairs, which include an imaging pixel pair provided withcolor filters of a different color from a color of color filtersprovided at the plural phase difference detection pixel pairs.

In the above aspect, the plural imaging pixel pairs may include one ormore imaging pixel pairs provided with R color filters, one or moreimaging pixel pairs provided with G color filters, and one or moreimaging pixel pairs provided with B color filters, and the secondcorrelation computation may include performing correlation computationon signals that are read from one or more imaging pixel pairs of theplural imaging pixel pairs which are configured from imaging pixelsprovided with color filters of a color having a signal level closest toa signal level of the phase difference detection pixels forming theplural phase difference detection pixel pairs.

The above aspect may further include: prior to the second correlationcomputation, selecting from the plural imaging pixel pairs, whichinclude one or more imaging pixel pairs provided with R color filters,one or more imaging pixel pairs provided with G color filters and one ormore imaging pixel pairs provided with B color filters, one or moreimaging pixel pairs formed from imaging pixels provided with colorfilters of a color having a signal level closest to a signal level ofthe phase difference detection pixels forming the plural phasedifference detection pixel pairs; and controlling the reading such thatsignals are read from the plural phase difference detection pixel pairsand the selected one or more imaging pixel pairs, wherein the secondcorrelation computation includes performing correlation computation onthe read signals.

The above aspect may to further include controlling an exposure time ofthe image pick-up device such that an exposure amount corresponds to thesensitivity of the imaging pixels.

The above aspect may further include: determining whether or notcorrection is to be performed based on at least one of: a size of afocal region for focus matching, a number of the phase differencedetection pixels from which signals used in the first correlationcomputation are read out, movement of a subject within an image captureangle, or movement of a subject within the focal region; and if it hasdetermined that correction is not to be performed, preventing executionof correction and performing focus control using the result of the firstcorrelation computation without correction.

Thus, since the correlation computation result of the signals read fromthe phase difference detection pixel pairs is corrected with thecorrelation computation result of the signals read from the imagingpixel pairs, the influence of distortion caused by the rolling shuttermethod is reduced, and it is possible to perform in-focus positiondetection and focus control at high precision, without providing anadditional circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described indetail based on the following figures, wherein:

FIG. 1 is a block diagram illustrating relevant configuration of anelectrical system of a digital camera according to an exemplaryembodiment;

FIG. 2 is a plan view illustrating an overall configuration of a CMOS;

FIG. 3 is an enlarged schematic diagram illustrating a portion of asurface of a phase difference detection region;

FIG. 4 is a diagram schematically illustrating only phase differencedetection pixels extracted from FIG. 3;

FIG. 5A is a diagram schematically illustrating that a shift amountderived by correlation computation on detection signals read from a pairof phase difference detection pixels contains not only a phasedifference amount but also an error amount due to rolling distortion(distortion amount caused by the rolling shutter method);

FIG. 5B is a schematic diagram illustrating that a distortion amountcaused by the rolling shutter method can be computed by performingcorrelation computation on signals from imaging pixels;

FIG. 6 is a flow chart illustrating a flow of AF control according to afirst exemplary embodiment;

FIG. 7 is a diagram illustrating an example of imaging pixel pairs usedfor computing a distortion amount caused by the rolling shutter method;

FIG. 8 is a diagram illustrating an example of imaging pixel pairs usedfor computing a distortion amount caused by the rolling shutter method;

FIG. 9 is a diagram illustrating an example of imaging pixel pairs usedfor computing a distortion amount caused by the rolling shutter method;

FIG. 10 is a diagram illustrating an example of imaging pixel pairs usedfor computing a distortion amount caused by the rolling shutter method;

FIG. 11 is graph illustrating an example of signal intensitiesrespectively read from phase difference detection pixels and G imagingpixels that are disposed diagonally-adjacent;

FIG. 12 is graph illustrating an example of levels of signal intensityof phase difference detection pixels A and levels of signal intensitiesrespectively read from imaging pixels provided with an R color filter(normal R pixels), imaging pixels provided with a G color filter (normalG pixels) and imaging pixels provided with a B color filter (normal Bpixels), which are disposed at the periphery of the phase differencedetection pixels A;

FIG. 13 is a flow chart illustrating an example of flow of AF controlprocessing according to a second exemplary embodiment;

FIG. 14 is a flow chart illustrating another example of flow of AFcontrol processing according to the second exemplary embodiment;

FIG. 15 is a flow chart illustrating another example of flow of AFcontrol processing according to the second exemplary embodiment;

FIG. 16 is a flow chart illustrating another example of flow of AFcontrol processing according to the second exemplary embodiment; and

FIG. 17 is a flow chart illustrating another example of flow of AFcontrol processing according to the second exemplary embodiment;

DETAILED DESCRIPTION

Hereinafter, explanation is given of embodiments in which the presentinvention is applied to a digital electronic still camera (called“digital camera” below) that performs imaging of a still image.

First Exemplary Embodiment

Firstly, explanation follows regarding relevant configuration of anelectrical system of a digital camera 10 according to the presentexemplary embodiment, with reference to FIG. 1.

As illustrated in FIG. 1, the digital camera 10 according to the presentexemplary embodiment includes: an optical unit 22 including lenses forfocusing a subject; a solid-state image pick-up device (a ComplementaryMetal Oxide Semiconductor (CMOS) in the present exemplary embodiment) 24that is disposed downstream to the lenses and on the optical axis of thelenses; and an analogue signal processor 26 that performs various typesof analogue signal processing on input analogue signals.

Moreover, the digital camera 10 includes: an analogue/digital converter(referred to below as ADC) 28 that converts input analogue signals intodigital signals; and a digital signal processor 30 that performs varioustypes of digital signal processing on input digital data.

The digital signal processor 30 is installed with a specific capacity ofline buffer, and also performs control of directly storing input digitaldata in a specific region of a memory 48 that is described later.

The output terminal of the CMOS 24 is connected to the input terminal ofthe analogue signal processor 26, the output terminal of the analoguesignal processor 26 is connected to the input terminal of the ADC 28,and the output terminal of the ADC 28 is connected to the input terminalof the digital signal processor 30. As a result, analogue signalsexpressing a subject image output from the CMOS 24 are subject tospecific analogue signal processing by the analogue signal processor 26,and are input to the digital signal processor 30 after being convertedinto digital image data by the ADC 28.

The digital camera 10 also includes: a Liquid Crystal Display (referredto below as LCD) 38 that displays captured subject images, menu screensand the like; an LCD interface 36 that generates signals for displayingthe captured subject images, menu screens and the like on the LCD 38,and supplies the signals to the LCD 38; a Central Processing Unit (CPU)40 that controls the overall operation of the digital camera 10; thememory 48 that temporarily stores data such as digital image dataobtained by imaging; and a memory interface 46 that performs accesscontrol for the memory 48.

Furthermore, the digital camera 10 includes: an external memoryinterface 50 for enabling access to a portable memory card 52 from thedigital camera 10; and a compression/decompression processing circuit 54that performs compression processing and decompression processing ondigital image data.

In the digital camera 10 of the present exemplary embodiment, a flashmemory (Flash Memory) is used as the memory 48, and an xD-Picture Card®is used as the memory card 52; however, embodiments are not limitedthereto.

The digital signal processor 30, the LCD interface 36, the CPU 40, thememory interface 46, the external memory interface 50, and thecompression/decompression processing circuit 54 are mutually connectedtogether by a system bus BUS. Consequently, the CPU 40 is able tocontrol operation of the digital signal processor 30 and thecompression/decompression processing circuit 54, to display various dataon the LCD 38 through the LCD interface 36, and to access the memory 48and the memory card 52 through the memory interface 46 and the externalmemory interface 50, respectively. Further, the CPU 40 executes AFcontrol, which is described later.

The digital camera 10 also includes a timing generator 32 that generatesa timing signal (pulse signal) mainly for driving the CMOS 24 andsupplies the timing signal to the CMOS 24. Driving of the CMOS 24 iscontrolled by the CPU 40 through the timing generator 32.

The CMOS 24 includes plural lines of plural pixels arrayed along thehorizontal direction, as described later. The CMOS 24 is controlled by arolling shutter method that controls an exposure start timing and a readtiming for each of the lines of the pixels. In the following explanationan example is given of a case in which the exposure start timing and theread timing are different for each line; however, embodiments are notlimited to this case.

The digital camera 10 also includes a motor driver 34. The CPU 40controls driving of a focus adjustment motor, a zoom motor, and anaperture drive motor, which are not illustrated in the drawings, and areprovided to the optical unit 22, through the motor driver 34.

The lenses according to the present exemplary embodiment include imaginglenses including a zoom lens and a focus lens, and the digital camera 10is provided with a lens drive mechanism, which is not illustrated in thedrawings. The focus adjustment motor, the zoom motor, and the aperturedrive motor are included in the lens drive mechanism. These motors arerespectively driven by drive signals supplied from the motor driver 34under control of the CPU 40.

The digital camera 10 also includes an operation section 56 includingvarious types of switch, such as: a release switch (called a shutter)that is pressed at execution of imaging; a power supply switch that isoperated to switch ON/OFF of the power supply to the digital camera 10;a mode switching switch that is operated to set one of the modes of animaging mode for performing imaging, or a reproduction mode forreproducing a subject on the LCD 38; a menu switch that is pressed todisplay menu screens on the LCD 38; a confirmation switch that ispressed to confirm previous operations; and a cancel switch that ispressed to cancel the last operation. The operation section 56 isconnected to the CPU 40. Accordingly, the CPU 40 is able to continuouslyascertain the operation state on the operation section 56.

The release switch of the digital camera 10 according to the presentexemplary embodiment is configured to enable two-stage press-operation:a state that is being pressed down to an intermediate position (referredto below as “half-pressed state”); and a state that is being presseddown beyond the indented position to the lowermost depressed position(referred to below as “fully-pressed state”).

In the digital camera 10, in response to the release switch being placedin the half-pressed state, an Automatic Exposure (AE) function isoperated and the exposure state (the shutter speed, aperture state) isset, and then focus control is performed by operation of the AFfunction. Then, in response to the release switch being placed in thefully-pressed state, exposure (imaging) is performed.

The digital camera 10 also includes a strobe 44 that emits light toilluminate the subject as required during imaging, and a charger 42 thatis interposed between the strobe 44 and the CPU 40 and that charges thestrobe 44 with power for light emission under control of the CPU 40. Thestrobe 44 is also connected to the CPU 40, and light emission of thestrobe 44 is controlled by the CPU 40.

FIG. 2 is a plan view illustrating an overall configuration of the CMOS24. An imaging region 70 of the CMOS 24 is formed by numerous pixels(light receiving elements, or photodiodes), which are not illustrated inthe drawings, disposed in a two dimensional array formation. In thepresent exemplary embodiment, pixel arrays are arranged in a honeycombarrangement, in which even-numbered pixel rows are shifted with respectto odd-numbered pixel rows by ½ the pixel pitch.

Further, although not illustrated in FIG. 2, in the present exemplaryembodiment, color filters of red (R), green (G) and blue (B) are appliedon each of the plural pixels of an imaging region 70 such that thepixels with different color layers are arranged in a Bayer arrangement.Alternatively, the arrangement of R, G, B color filters may beconfigured in a stripe arrangement.

The CMOS 24 is also provided with horizontal scanning circuits 72 ₁, 72₂ and vertical scanning circuits 74 ₁, 74 ₂ (corresponding to readingsections). While not illustrated in the drawings, horizontal signallines are connected to the horizontal scanning circuits 72 ₁, 72 ₂, andvertical selection lines are connected to the vertical scanning circuits74 ₁, 74 ₂.

The vertical scanning circuit 74 ₁ selects, in row (line) units, each ofthe pixels of a first pixel group of odd-numbered rows disposed in theimaging region 70 using the vertical selection lines. The selection isperformed by selecting the rows one by one in sequence from thelowermost row, and reading is performed for all the pixel signals ineach row together at one time. A CDS circuit may be provided in order toreduce reset noise by performing correlated double sampling processingon each of the pixel signals read in row units from the first pixelgroup. The horizontal scanning circuit 72 ₁ takes one row's worth ofpixel signals read from the first pixel group and selects the pixels oneby one in sequence from the left side. Each of the pixel signals readfrom the first pixel group is thereby output to the horizontal signallines. The pixel signals sequentially output in this manner to thehorizontal signal lines are amplified by an amplifier at the subsequentstage (not illustrated in the drawings) and then are output to externaldevices.

Further, the vertical scanning circuit 74 ₂ selects each of the pixelsof a second pixel group of even-numbered rows disposed in the imagingregion 70 in row units using the vertical selection lines. The selectionis performed by selecting the rows one by one in sequence from thelowermost row, and reading is performed for all the pixel signals ofeach row together at one time. A CDS circuit may be provided in order toreduce reset noise by performing correlated double sampling processingon each of the pixel signals read in row units from the second pixelgroup. The horizontal scanning circuit 72 ₂ takes one row's worth ofpixel signals read from the second pixel group and selects the pixelsone by one in sequence from the left side. Each of the pixel signalsread from the second pixel group is thereby output to the horizontalsignal lines. The pixel signals sequentially output in this manner tothe horizontal signal lines are amplified by an amplifier at thesubsequent stage (not illustrated in the drawings) and then are outputto external devices.

In the present exemplary embodiment, a rectangular shaped phasedifference detection region is provided in a part of the imaging region70, for example at a central position. The phase difference detectionregion may be provided only in one location of the imaging region 70, ormay be provided at plural locations so that AF function can be performedanywhere within the imaging region 70. Alternatively, the entire regionof the imaging region 70 may be configured as the phase differencedetection region.

FIG. 3 is an enlarged schematic diagram illustrating a portion of thesurface of the phase difference detection region. As described above,numerous pixels are disposed in a honeycomb arrangement in the imagingregion 70 of the CMOS 24. Similarly, in the phase difference detectionregion, pixels are disposed in a honeycomb arrangement, in whicheven-numbered pixel rows are shifted with respect to odd-numbered pixelrows by ½ the pixel pitch. Phase difference detection pixels 1x, 1y; andimaging pixels (pixels other than the phase difference detection pixels1x, 1y that are not provided with a light-blocking film and are ordinarypixels used for imaging the subject) are disposed in the phasedifference detection region. Moreover, although omitted fromillustration, only the imaging pixels are disposed in the imaging region70 other than in the phase difference detection region.

In the example illustrated in the drawings, each of the pixels isindicated by red (R), green (G) or blue (B). R, G, B represents thecolor of the color filter applied on each of the pixels. Moreover, thecolor filters for the odd-numbered row pixels are arrayed in a Bayerarrangement, and the color filters for the even-numbered row pixels arealso arrayed in a Bayer arrangement. Accordingly, when taking the twophase difference detection pixels 1x, 1y adjacent to each otherdiagonally as a single group (pair), color filters of the same color aredisposed on the two diagonally adjacent phase difference detectionpixels 1x, 1y constituting the pair. Similarly, for the imaging pixels,when taking two diagonally adjacent imaging pixels as a pair, colorfilter of the same color are disposed for the two diagonally adjacentimaging pixels constituting the pair. As illustrated in the drawings, inthe present exemplary embodiment, the pairs of phase differencedetection pixels are provided at cyclical and discrete positionsdistributed within the phase difference detection region.

In the present exemplary embodiment, the phase difference detectionpixels 1x, 1y are provided at the G filter pixels, which are the mostcommon among R, G, B filter pixels. The pair of phase differencedetection pixels 1x, 1y is disposed for every eight pixels in thehorizontal direction (the x-direction), and for every eight pixels inthe vertical direction (the y-direction), so that they are generallydisposed in a checkerboard (uniform) pattern.

Moreover, light-blocking film openings 2x, 2y of the phase differencedetection pixels 1x, 1y are formed smaller than the imaging pixels. Thelight-blocking film opening 2x of the pixel 1x provided eccentrically inthe left direction, and the light-blocking film opening 2y of the pixel1y provided eccentrically in the right direction (the phase differencedetection direction).

Due to adopting such a configuration, a light beam that has passedthrough an opening eccentric to one side (in this case the left side)with respect to the main axis of the imaging lens is incident to thephase difference detection pixel 1x. Moreover, a light beam that haspassed through an opening that is disposed on a line adjacent to thephase difference detection pixel 1x constituting the pair and that iseccentric to the other side (in this case the right side) with respectto the main axis of the imaging lens is incident to the phase differencedetection pixel 1y. Thus the light beams that have passed through to thephase difference detection pixels 1x, 1y have beam axes that are shiftedto the opposite sides from each other with respect to the main axis(note that in the vicinity of the main axis there may be some overlapbetween the light beams). As described later, since shifts in positionand phase of an image detected at each of the phase difference detectionpixels 1x, 1y arise in an out-of-focus state, focus control may beperformed by detecting this shift amount (phase difference amount).

The phase difference detection pixels 1x, 1y can be used not only forphase difference detection for AF control but also be used for imageformation of a subject.

FIG. 4 is a diagram schematically illustrating only the phase differencedetection pixels 1x, 1y that have been extracted from FIG. 3. The curveX at the bottom of FIG. 4 is a graph plotting the detection signalintensity of the phase difference detection pixels 1x arrayed in an asingle row, and curve Y is a graph plotting the detection signalintensity of the phase difference detection pixels 1y that are pairedwith these pixels 1x.

Since the phase difference detection pixels 1x, 1y that configure asingle pair are adjacent pixels that are extremely close to each other,it is considered that they receive light from the same subject.Therefore, the curve X and the curve Y should be substantially the sameshape as each other as long as there is no influence from distortioncaused by the rolling shutter method, which is described later. Theshift in the left-right direction (the phase difference detectiondirection) is a phase difference amount between an image viewed from thephase difference detection pixel 1x that is one of the pupil-dividedpair and an image viewed from the other pixel 1y.

The horizontal shift amount (phase difference amount) can be derived bycomputing the correlation between the curve X and the curve Y, and thedistance from the device to the subject can be computed from this phasedifference. A known method (for example, the method disclosed in JP-ANo. 2010-8443 or the method disclosed in JP-A No. 2010-91991) may beused to derive an evaluation value of a phase difference between thecurve X and the curve Y. For example, the integral value of the absolutevalue of the difference between each of the points X (i) forming thecurve X and each of the points Y (i+j) forming the curve Y may be takenas evaluation values and the j value that gives the maximum evaluationvalue may be taken as the phase difference.

Then the motor driver 34 may be controlled based on the distance fromthe device to the subject derived from the phase difference, and thefocus adjustment motor of the optical unit 22 may be driven to controlthe position of the focus lens so as to focus on the subject.

However, the present exemplary embodiment uses a CMOS controlled by arolling shutter method as the solid-state image pick-up device. Thus, ina case in which a correlation computation is performed on detectionsignals acquired from a phase difference detection pixel pair,configured from two diagonally adjacent phase difference detectionpixels that are not read at the same time, distortion in the subjectimage being imaged arises if the subject has moved or changed during thedifferent timings of read-out of the phase difference detection pixels,and an influence of distortion (distortion amount) caused by the rollingshutter method arises in the phase difference amount derived in thecorrelation computation (see also FIG. 5A).

In this regard, as illustrated in FIG. 5B, by taking, for example, twodiagonally adjacent imaging pixels of the same color (indicated asimaging pixels A, B in FIG. 5B) as a group (pair), and performingcorrelation computation on the detection signals of this pair, only thedistortion amount caused by the rolling shutter method can be computed,since there is no light-blocking film left-right eccentrically providedon each of the imaging pixels. In the present exemplary embodiment, AFcontrol is performed by correcting the phase difference amounts derivedfrom the phase difference detection pixels using the detection signal ofthe imaging pixels.

FIG. 6 is a flow chart illustrating a flow of AF control according tothe present exemplary embodiment. During reading of detection signalsfrom the phase difference detection pixels and the imaging pixels forperforming AF control, the detection signals are read from the pixels inline units without discrimination between phase difference detectionpixels and imaging pixels.

At step 100, correlation computation is performed on the detectionsignals (hereinafter also referred to as phase difference detectionpixel signals) read from plural phase difference detection pixel pairs,and a phase difference amount is derived (the CPU 40 functions as afirst correlation computation section).

At step 102, correlation computation is performed on the detectionsignals (hereinafter also referred to as imaging pixel signals) readfrom plural imaging pixel pairs, and the distortion amount caused by therolling shutter method is derived (the CPU 40 functions as a secondcorrelation computation section). In this case, as illustrated in FIG.7, the distortion amount is derived by performing correlationcomputation on the detection signals read from the imaging pixel pairs Pconfigured from the adjacent imaging pixels having filters of the samecolor as that of the phase difference detection pixels (in this case Gfilters) and disposed between phase difference detection pixels pairsthat are disposed next to each other in the horizontal direction.Namely, in the present exemplary embodiment, looking at pairs formedwith G filters, the imaging pixel pairs and the phase differencedetection pixel pairs of G color are disposed alternately to each otherin the horizontal direction. Consequently, in this case, the color Gphase difference detection pixel pairs and the alternately disposedcolor G imaging pixel pairs are used to derive the distortion amount.

At step 104, the phase difference amount derived at step 100 iscorrected by subtracting the distortion amount derived at step 102 fromthe phase difference amount detected at step 100 (the CPU 40 functionsas a correction section)

At step 106, focus control is performed as described above based on thecorrected phase difference amounts (the CPU 40 functions as a focusingsection).

As described above, correlation computation results from the phasedifference detection pixel signals are corrected with the correlationcomputation results of the normal pixel signals so as to perform AFcontrol. Accordingly, the influence of distortion caused by the rollingshutter method is reduced, and AF control can be performed at highprecision.

Note that the imaging pixels for computing the distortion amount causedby the rolling shutter method are not limited to those illustrated inFIG. 7. For example, as illustrated in FIG. 8, the distortion amount maybe derived by performing correlation computation on detection signalsread from imaging pixel pairs P that are disposed between phasedifference detection pixel pairs that are disposed next to each other inhorizontal direction, and that have filters of a different color tothose of the phase difference detection pixels. That is, the imagingpixel pairs P are configured from adjacent imaging pixels disposed onthe same lines on which the phase difference detection pixels of thephase difference detection pixel pairs are disposed, and the imagingpixel pairs P have filters of a different color to those of the phasedifference detection pixel pairs. In this way, even in cases in whichthere are no imaging pixel pairs having the same color filters betweenthe phase difference detection pixels disposed next to each other inhorizontal direction, it is possible to compute the phase differenceamount at high precision by computing the distortion amount. The casesin which there are no imaging pixel pairs having the same color filtersbetween the phase difference detection pixels disposed next to eachother in horizontal direction include, for example, cases in which thephase difference detection pixels are disposed with an interval of fourpixels in the horizontal direction (the x direction), or cases in whichthe placement of color filters on the pixels is different to thatillustrated in FIG. 3.

Or, the distortion amount may be derived from detection signals readfrom imaging pixel pairs P configured by G imaging pixels that aredisposed on different lines from the phase difference detection pixels1x, 1y, and wherein the positions of the G imaging pixels from one endof the line are the same as the phase difference detection pixels 1x, 1y(that is, G imaging pixels that are disposed in a vertical direction ofthe phase difference detection pixel pairs).

Alternatively, as illustrated in FIG. 9, the distortion amount may bederived from detection signals read from imaging pixel pairs Pconfigured by G imaging pixels adjacent to the phase differencedetection pixels 1x, 1y, which are disposed on different lines from thephase difference detection pixels 1x, 1y, and wherein the positions ofthe G imaging pixels from one end of the line are different from thephase difference detection pixels 1x, 1y (that is, G imaging pixel pairsP that are disposed diagonally adjacent with respect to the phasedifference detection pixel pairs). Or, as illustrated in FIG. 10, thedistortion amount may be derived using G imaging pixel pairs P that aredisposed in a vertical direction of the phase difference detectionpixels, and G imaging pixel pairs P that are disposed in a diagonaldirection thereof.

Namely, the respective imaging pixels constituting the imaging pixelpairs may be disposed in lines that are different from the lines inwhich the phase difference detection pixels of the phase differencedetection pixel pairs are disposed. Accordingly, imaging pixel pairsused for computing the distortion amount may be increased by usingimaging pixel pairs disposed on lines that are different from lines onwhich the phase difference detection pixel pairs are disposed (namely,imaging pixel pairs disposed in the vertical direction and/or thediagonal direction of phase difference detection pixel pairs). In thisway, the density of imaging pixels for each horizontal line may beraised, and the computing precision of the distortion amount isimproved.

In conventional AF control, phase difference detection is performedwhile an exposure control is performed to adjust the exposure amount inaccordance with the sensitivity of the phase difference detectionpixels. However, in cases in which AF control is performed as in thepresent exemplary embodiment, the exposure time may be controlled so asto adjust the exposure amount in accordance with the sensitivity of theimaging pixels (the CPU 40 functions as an exposure control section).

FIG. 11 is a graph illustrating an example of signal intensitiesrespectively read from phase difference detection pixels and adjacent Gimaging pixels that are disposed in a diagonal direction. In the phasedifference detection pixels light-blocking film openings are formedsmaller than those of the imaging pixels, and hence, as illustrated inFIG. 11, the sensitivity of the phase difference detection pixels islower than the sensitivity of the imaging pixels. Therefore, in the AFcontrol of the present exemplary embodiment, the exposure time iscontrolled such that the exposure amount for each of the pixels is givenin accordance with the sensitivity of the imaging pixels, rather than inaccordance with the sensitivity of the phase difference detectionpixels. Accordingly, the computation precision with the imaging pixelsmay be improved.

Moreover, in cases in which the imaging pixels used for computing thedistortion amount are not limited to the imaging pixels provided withcolor filters of the same color as those of the phase differencedetection pixels, the detection signals read from each of the imagingpixels provided with a R filter, the imaging pixels provided with the Gfilters, and the imaging pixels provided with a B filter, which aredisposed in the vicinity of the phase difference detection pixels, andthe detection signals read from the phase difference detection pixelsare mutually compared. Then, computation of the distortion amount may beperformed by selecting and using pairs of imaging pixels of the colorthat have the closest sensitivity to the phase difference detectionpixels (i.e., selecting imaging pixels provided with color filtershaving the nearest level of signal intensity (signal level) to the levelof the detection signals of the phase difference detection pixels) (theCPU 40 functions as a selection section and a read control section).

FIG. 12 is a graph illustrating an example of signal levels of the phasedifference detection pixels A, and signal levels read from each ofimaging pixels provided with a R filter (normal R pixels), imagingpixels provided with G filters (normal G pixels), and imaging pixelsprovided with a B filter (normal B pixels), which are disposed in thevicinity of the phase difference detection pixels A. It can be seen inthe example illustrated in FIG. 12 that among the normal R pixels, thenormal G pixels, and the normal B pixels, the signal level of the normalB pixels is the closest to the signal level of the phase differencedetection pixels A. Consequently, in this example, computation ofdistortion amount is performed using the pairs of normal B pixels.

Thus, sufficient signal intensity can be achieved for both the imagingpixels and the phase difference detection pixels, which may improve theprecision of phase difference detection.

This method can be similarly applied to the cases illustrated in FIG. 9and FIG. 10. That is, also in cases in which the distortion amount iscomputed using the imaging pixel pairs disposed in the verticaldirection or the diagonal direction of the phase difference detectionpixel pairs, the distortion amount may be computed using the imagingpixel pairs of the color having the nearest signal level to that of thephase difference detection pixel pairs.

Further, the colors of the subject image may be detected prior to AFcontrol, the signal level of the phase difference detection pixels maybe compared to the signal level of each of the colors R, G, B, and thecolor having a signal level that is closest to that of the phasedifference detection pixels may be selected, and data thereof may bestored in advance. Then, during AF control, detection signals may beread from the imaging pixel pairs of the color indicated by the storeddata and from the phase difference detection pixel pairs, and the readsignals may be used in the phase difference detection as describedabove.

For example, since white balance correction includes a process ofdetecting the signals of each of the colors R, G, B, white balancecorrection may be performed prior to AF control in order to check thesignal intensities of each of the colors, and the color with the nearestsignal intensity to the phase difference detection pixels may beselected and stored in advance for use during AF control.

In this way, since there is no need to read the detection signal fromall the colors of imaging pixels at the AF control stage, the timerequired for reading detection signals can be reduced, and thecomputation of the distortion amount may be performed at high precision.

Embodiments are not limited to the present exemplary embodiment in whichrolling correction is always performed. For example, a switching sectionthat switches between a first mode in which rolling correction isperformed in AF control and a second mode in which rolling correction isnot performed may be provided, and AF control may be performed accordingto the mode switched by a user using the switching section.

Second Exemplary Embodiment

The first exemplary embodiment has given an example in which distortionamount computation and correction is always performed during AF control.However, in cases in which it is expected that distortion caused by therolling shutter method has relatively small influence, computing processof the distortion amount and correction process may be omitted. Detailedexplanation thereof follows.

Since the configuration of the digital camera 10 of the presentexemplary embodiment is similar to that of the first exemplaryembodiment, explanation thereof is omitted.

FIG. 13 is a flow chart illustrating an example flow of AF controlprocessing according to the present exemplary embodiment.

At step 200, correlation computation is performed on the phasedifference detection pixel signals as explained in the first exemplaryembodiment, and the phase difference amount is derived.

At step 202, determination is made as to whether or not the size of anAF region is equal to or greater than a predetermined threshold value.The AF region is a region for focus matching, and there are cases inwhich the digital camera 10 is configured to allow a user to set adesired position or size of the AF region, or cases in which the size ofthe AF region is set according to the imaging mode. In the presentexemplary embodiment, data indicating the size of the AF region set inthe digital camera 10 is acquired, and is compared with a predeterminedthreshold value (the CPU functions as a determination section).

If a positive determination has been made at step 202, then at step 204the correlation computation on imaging pixel signals is performed asexplained in the first exemplary embodiment, and the distortion amountis determined. At step 206, the phase difference amount derived at step200 is corrected by subtracting the distortion amount derived at step204 from the phase difference amount derived at step 200. At step 208,focus control is performed based on the corrected phase differenceamount.

However, if a negative determination has been made at step 202, steps204 and 206 are skipped, and the processing proceeds to step 208. Insuch cases, focus control is performed at step 208 by directly using thephase difference amount derived at step 200 (i.e., using the phasedifference amount that is not corrected by a distortion amount).

In cases in which the AF region is not relatively large, the number ofphase difference detection pixels for detection signal reading is smalland the influence of distortion caused by the rolling shutter method isexpected to be small. Thus, in the present exemplary embodiment, incases in which the size of the AF region is less than the thresholdvalue, AF control is performed without performing the distortion amountcomputation process and the correction process. Thereby, the timerequired for AF control can be reduced.

FIG. 14 is a flow chart illustrating another example of a flow of AFcontrol processing.

In step 300, correlation computation on the phase difference detectionpixel signals is performed as explained in the first exemplaryembodiment and the phase difference amount is then derived.

In step 302, determination is made as to whether or not the number ofread pixels (i.e., the number of phase difference detection pixels fromwhich detection signals are read) is equal to or greater than apredetermined threshold value. If a positive determination has been madeat step 302, at step 304 correlation computation on the imaging pixelsignals is performed and the distortion amount is derived as explainedin the first exemplary embodiment. At step 306, the phase differenceamount derived at step 300 is corrected by subtracting the distortionamount derived at step 304 from the phase difference amount derived atstep 300. Then focus control is performed at step 308 based on thecorrected phase difference amount.

However, if a negative determination has been made at step 302, steps304 and 306 are skipped, and the processing proceeds to step 308. Insuch cases, focus control is performed at step 308 by directly using thephase difference amount derived at step 300 (i.e., using the phasedifference amount that is not corrected by a distortion amount).

In cases in which the number of phase difference detection pixels forreading detection signals (namely, the number of phase differencedetection pixel used at step 300 to compute the phase difference amount)is small, the influence of distortion caused by the rolling shuttermethod is expected to be small. Thus, in the present example, in casesin which the number of phase difference detection pixels for readingdetection signals is less than the threshold value, AF control isperformed without performing the distortion amount computation processand the correction process. Thereby, the time required for AF controlcan be reduced.

The threshold values used in the embodiments illustrated in FIG. 13 andFIG. 14 may be changed according to the image angle. Specifically, forexample, in a case in which the digital camera 10 is configured to allowselection of a wide angle mode, a normal mode, or a telephoto mode, athreshold value may be set in advance for each of the modes, and thethreshold value described above may be changed according to the imagingmode that has been set when AF control is performed. Since the influenceof the distortion caused by the rolling shutter method is expected to begreater as the image angle is set toward the telephoto side, thethreshold value may be set smaller at the telephoto side than the wideangle side.

FIG. 15 is a flow chart illustrating another example of AF controlprocessing.

At step 400, correlation computation on the phase difference detectionpixel signals is performed as explained in the first exemplaryembodiment, and the phase difference amount is derived.

At step 402, determination is made as to whether or not a distance tothe subject is equal to or greater than a predetermined threshold value.In this case, the distance to the subject that is provisionally derivedfrom the phase difference derived at step 400 is compared with thepredetermined threshold value. The threshold value for comparison may bechanged according to the size of the AF region or the number of readpixels. If a positive determination has been made at step 402,correlation computation on the imaging pixel signals is performed andthe distortion amount is derived at step 404 as explained in the firstexemplary embodiment. At step 406, the phase difference amount derivedat step 400 is corrected by subtracting the distortion amount derived atstep 404 from the phase difference amount derived at step 400. Then, atstep 408, focus control is performed based on the corrected phasedifference amount.

However, if a negative determination has been made at step 402, steps404 and 406 are skipped, and the processing proceeds to step 408. Insuch cases, at step 408 focus control is performed directly using thephase difference amount derived at step 400 (i.e., using the phasedifference amount that is not corrected by a distortion amount).

The degree of influence caused by the rolling shutter method variesdepending on the movement of a subject within the image capture angle.In particular, the influence of distortion caused by the rolling shuttermethod is expected to be larger as the distance to the subject islonger. Thus, in the present exemplary, of the distortion amountcomputation process and the correction process are performed in cases inwhich the distance to the subject is equal to or longer than thethreshold value, and are not performed in cases which the distance tothe subject is shorter than the threshold value.

FIG. 16 is a flow chart illustrating another example of flow of AFcontrol processing.

At step 500, correlation computation on the phase difference detectionpixel signals is performed as explained in the first exemplaryembodiment and the phase difference amount is then derived.

In step 502, detection of a moving body in the image angle is performed.For example, movement vectors between past image data stored in thememory 48 and current image data may be computed using a known method,and the detection may be performed based on the magnitude of themovement vector.

At step 504, determination is made as to whether or not there is amoving body present in the image angle based on the detection result. Ifa positive determination has been made at step 504, at step 506, thedistortion amount is derived by performing correlation computation onthe imaging pixel signals as explained in the first exemplaryembodiment. At step 508, the phase difference amount derived at step 500is corrected by subtracting the distortion amount derived at step 506from the phase difference amount derived at step 500. Then, at step 510,focus control is performed based on the corrected phase differenceamount.

If a negative determination has been made at step 504, step 506 and step508 are skipped, and the processing proceeds to step 510. In such cases,focus control is performed at step 510 directly using the phasedifference amount derived at step 500 (i.e., using the phase differenceamount that is not corrected by a distortion amount).

The distortion caused by the rolling shutter method occurs in cases inwhich a moving body is present in the image capture angle. Thus, in thepresent example, a moving body is detected, and the distortion amountcomputation process and the correction process are performed only incases in which a moving body is present, and are not performed in casesin which a moving body is not present.

FIG. 17 is a flow chart illustrating another example of flow of AFcontrol processing.

At step 600, correlation computation on the phase difference detectionpixel signals is performed as explained in the first exemplaryembodiment and the phase difference amount is then derived.

In step 602, detection for a moving body in the AF region is performed.For example, movement vectors between past image data stored in thememory 48 and current image data may be computed using a known method,and the detection of moving body may be performed based on the magnitudeof the movement vector.

At step 604, determination is made as to whether or not there is movingbody present in the AF region based on the detection result. If apositive determination has been made at step 602, at step 606, thedistortion amount is derived by performing correlation computation onthe imaging pixel signals as explained in the first exemplaryembodiment. At step 608, the phase difference amount derived at step 600is corrected by subtracting the distortion amount derived at step 606from the phase difference amount derived at step 600. Then, at step 610,focus control is performed based on the corrected phase differenceamount.

However, if a negative determination has been made at step 604, steps606 and 608 are skipped, and the processing proceeds to step 610. Insuch cases, at step 610, focus control is performed directly using thephase difference amount derived at step 600 (i.e., using the phasedifference amount that is not corrected by a distortion amount).

The distortion caused by the rolling shutter method occurs in cases inwhich a moving body is present in the image capture angle. Thus, in thepresent example, a moving body is detected in particular in the AFregion, and the distortion amount computation process and the correctionprocess are performed only in cases in which a moving body is present inthe AF region, and are not performed in cases in which a moving body isnot present.

As explained above, in the present exemplary embodiment, in cases inwhich the influence of distortion caused by the rolling shutter methodis expected to be small, the distortion amount computation andcorrection are not performed, and are performed in other cases.Consequently, unnecessary time can be saved during AF control, whilepreventing the influence of distortion caused by the rolling shuttermethod.

Embodiments are not limited to the present exemplary embodiment in whicha determination of performing the distortion amount computation andcorrection is made according to one of the size of the AF region, thenumber of read pixels, the distance to the subject, movement of thesubject in the image capture angle, or movement of the subject in the AFregion. For example, the determination of performing the distortionamount computation and correction may be made according to at least oneof the size of the AF region, the number of read pixels, the distance tothe subject, movement of the subject in the image capture angle, and/ormovement of the subject in the AF region.

The digital camera 10 may include a switching section that switchesbetween a first mode in which rolling correction is always performed asin the first exemplary embodiment, and a second mode in which rollingcorrection is not performed if it is expected that the influence fromdistortion caused by the rolling shutter method is small as in thesecond exemplary embodiment. In such cases, AF control may be performedaccording to the mode switched to by a user using the switching section.

Further, the phase difference detection pixels 1x, 1y are not limited tothe examples illustrated in the respective exemplary embodimentsdescribed above. For example, the phase difference detection pixel 1xmay be configured such that light is blocked at the right half and isopen at the left half, and the phase difference detection pixel 1y maybe configured such that light is blocked at the left half and is open atthe right half. Using such configured phase difference detection pixels,similarly to the embodiments described above, a light beam that haspassed through one side (in this case the left side) with respect to themain axis of the imaging lens is incident to the phase differencedetection pixel 1x, and a light beam that has passed through the otherside (the right side) with respect to the main axis of the imaging lensis incident to the phase difference detection pixel 1y.

Further, embodiments are not limited to the configurations of the firstand second exemplary embodiment in which the phase difference detectionpixels constituting the phase difference detection pixel pairs areadjacent pixels. The phase difference detection pixels constituting thephase difference detection pixel pairs may not be adjacent to eachother, and one or more pixels may be disposed between the pixelsconstituting the pairs. Embodiments are also not limited to theconfiguration in which the imaging pixels constituting the imaging pixelpairs are adjacent pixels. The imaging pixels constituting the imagingpixel pairs may not be adjacent to each other, and one or more pixelsmay be disposed between the pixels constituting the pairs.

Embodiments are not limited to the cases in the first exemplaryembodiment and the second exemplary embodiment, which describeapplications a digital camera. For example, embodiments are possible inwhich application is made to other devices that include imagingfunctions, such as mobile phones, PDAs and the like. Similar effects tothose of the exemplary embodiments described above can also be exhibitedin such cases.

The flow of processing in each of the processing programs explained inthe exemplary embodiments are merely examples, and modifications withina range not departing from the spirit of the present invention such aschanging the processing sequence of each step, changing the contents ofthe processing, eliminating unnecessary steps for actual implementation,or adding new steps are obviously possible.

What is claimed is:
 1. An imaging device comprising: an image pick-updevice comprising a plurality of phase difference detection pixel pairs,each formed from a first phase difference detection pixel and a secondphase difference detection pixel, each of which forms a pupil-dividedimage from a subject image that has passed through a first region and asecond region of an imaging lens, and a plurality of imaging pixel pairsincluding a plurality of imaging pixels; a reading section that performsread-out with respect to the image pick-up device by reading signalsfrom the imaging pixels and the phase difference detection pixelsarrayed in the image pick-up device using a rolling shutter method; afirst correlation computation section that performs correlationcomputation on the signals that have been read from the phase differencedetection pixel pairs; a second correlation computation section thatperforms correlation computation on the signals that have been read fromthe imaging pixel pairs; a correction section that corrects acorrelation computation result from the first correlation computationsection using a correlation computation result from the secondcorrelation computation section; and a focusing section that performsfocus control using the corrected correlation computation result.
 2. Theimaging device of claim 1, wherein the second correlation computationsection performs correlation computation on signals read from theplurality of imaging pixel pairs, each of which is formed from: animaging pixel disposed on a line on which the first phase differencedetection pixel of one of the plurality of phase difference detectionpixel pairs is disposed, and an imaging pixel disposed on a line onwhich the second phase difference detection pixel of the one of theplurality of phase difference detection pixel pairs is disposed.
 3. Theimaging device of claim 1, wherein the second correlation computationsection performs correlation computation on signals read from theplurality of imaging pixel pairs, each of which are formed from imagingpixels that are disposed on lines that are different from the lines onwhich the phase difference detection pixels of the plurality of phasedifference detection pixel pairs are disposed.
 4. The imaging device ofclaim 1, wherein the second correlation computation section performscorrelation computation on signals read from the plurality of imagingpixel pairs provided with color filters of a same color as a color ofcolor filters provided at the plurality of phase difference detectionpixel pairs.
 5. The imaging device of claim 1, wherein the secondcorrelation computation section performs correlation computation onsignals read from the plurality of imaging pixel pairs, which include animaging pixel pair provided with color filters of a different color froma color of color filters provided at the plurality of phase differencedetection pixel pairs.
 6. The imaging device of claim 1, wherein theplurality of imaging pixel pairs comprise one or more imaging pixelpairs provided with R color filters, one or more imaging pixel pairsprovided with G color filters, and one or more imaging pixel pairsprovided with B color filters, and the second correlation computationsection performs correlation computation on signals that are read fromone or more imaging pixel pairs of the plurality of imaging pixel pairswhich are formed from imaging pixels provided with color filters of acolor having a signal level closest to a signal level of the phasedifference detection pixels forming the plurality of phase differencedetection pixel pairs.
 7. The imaging device of claim 1, furthercomprising: a selection section that, prior to the correlationcomputation performed by the second correlation computation section,selects from the plurality of imaging pixel pairs, which comprise one ormore imaging pixel pairs provided with R color filters, one or moreimaging pixel pairs provided with G color filters and one or moreimaging pixel pairs provided with B color filters, one or more imagingpixel pairs formed from imaging pixels provided with color filters of acolor having a signal level closest to a signal level of the phasedifference detection pixels forming the plurality of phase differencedetection pixel pairs; and a control section that controls the readingsection such that signals are respectively read from the plurality ofphase difference detection pixel pairs and the one or more imaging pixelpairs selected by the selection section, wherein the second correlationcomputation section performs the correlation computation on the signalsread under control of the control section.
 8. The imaging device ofclaim 1, further comprising an exposure control section that controls anexposure time of the image pick-up device such that an exposure amountcorresponds to the sensitivity of the imaging pixels.
 9. The imagingdevice of claim 1, further comprising: a determination section thatdetermines whether or not correction is to be performed by thecorrection section based on at least one of: a size of a focal regionfor focus matching, a number of the phase difference detection pixelsfrom which signals used in correlation computation by the firstcorrelation computation section are read out, movement of a subjectwithin an image capture angle, or movement of a subject within the focalregion, wherein, if the determination section determines that correctionis not to be performed by the correction section, the focusing sectionprevents execution of the correction by the correction section andperforms focus control using the correlation computation result from thefirst correlation computation section without correction.
 10. A focusingcontrol method for an imaging device comprising an image pick-up devicecomprising a plurality of phase difference detection pixel pairs eachformed from a first phase difference detection pixel having a firstopening formed at one side with respect to a main axis of an imaginglens and at which a light beam that has passed through the first openingis incident, and a second phase difference detection pixel having asecond opening formed at the other side with respect to the main axisand at which a light beam that has passed through the second opening isincident, and a plurality of imaging pixel pairs including a pluralityof imaging pixels, the focusing control method comprising: performingreading-out to the image pick-up device by reading signals from theimaging pixels and the phase difference detection pixels arrayed in theimage pick-up device using a rolling shutter method; performing a firstcorrelation computation on the signals that have been read from theplurality of phase difference detection pixel pairs; performing a secondcorrelation computation on the signals that have been read from theplurality of imaging pixel pairs; correcting a result of the firstcorrelation computation using a result of the second correlationcomputation; and performing focus control using the corrected result ofthe correlation computations.
 11. The focusing control method of claim10, wherein the second correlation computation comprises performingcorrelation computation on signals read from the plurality of imagingpixel pairs, each of which is formed from: an imaging pixel disposed ona line on which the first phase difference detection pixel of one of theplurality of phase difference detection pixel pairs is disposed, and animaging pixel disposed on a line on which the second phase differencedetection pixel of the one of the plurality of phase differencedetection pixel pairs is disposed.
 12. The focusing control method ofclaim 10, wherein the second correlation computation comprisesperforming correlation computation on signals read from the plurality ofimaging pixel pairs each formed from imaging pixels that are disposed onlines that are different from lines on which the phase differencedetection pixels of the plurality of phase difference detection pixelpairs are disposed.
 13. The focusing control method of claim 10, whereinthe second correlation computation comprises performing correlationcomputation on signals read from the plurality of imaging pixel pairs,which are provided with color filters of a same color as a color ofcolor filters provided at the plurality of phase difference detectionpixel pairs.
 14. The focusing control method of claim 10, wherein thesecond correlation computation comprises performing correlationcomputation on signals read from the plurality of imaging pixel pairs,which include an imaging pixel pair provided with color filters of adifferent color from a color of color filters provided at the pluralityof phase difference detection pixel pairs.
 15. The focusing controlmethod of claim 10, wherein the plurality of imaging pixel pairscomprise one or more imaging pixel pairs provided with R color filters,one or more imaging pixel pairs provided with G color filters, and oneor more imaging pixel pairs provided with B color filters, and thesecond correlation computation comprises performing correlationcomputation on signals that are read from one or more imaging pixelpairs of the plurality of imaging pixel pairs which are configured fromimaging pixels provided with color filters of a color having a signallevel closest to a signal level of the phase difference detection pixelsforming the plurality of phase difference detection pixel pairs.
 16. Thefocusing control method of claim 10, further comprising: prior to thesecond correlation computation, selecting from the plurality of imagingpixel pairs, which comprise one or more imaging pixel pairs providedwith R color filters, one or more imaging pixel pairs provided with Gcolor filters and one or more imaging pixel pairs provided with B colorfilters, one or more imaging pixel pairs formed from imaging pixelsprovided with color filters of a color having a signal level closest toa signal level of the phase difference detection pixels forming theplurality of phase difference detection pixel pairs; and controlling thereading such that signals are read from the plurality of phasedifference detection pixel pairs and the selected one or more imagingpixel pairs, wherein the second correlation computation comprisesperforming correlation computation on the read signals.
 17. The focusingcontrol method of claim 10, further comprising controlling an exposuretime of the image pick-up device such that an exposure amountcorresponds to the sensitivity of the imaging pixels.
 18. The focusingcontrol method of claim 10, further comprising: determining whether ornot correction is to be performed based on at least one of: a size of afocal region for focus matching, a number of the phase differencedetection pixels from which signals used in the first correlationcomputation are read out, movement of a subject within an image captureangle, or movement of a subject within the focal region; and if it hasdetermined that correction is not to be performed, preventing executionof correction and performing focus control using the result of the firstcorrelation computation without correction.